1. Field of the Invention
The present invention relates, generally, to electronic instrumentation such as electronic flight control instrumentation and, more particularly, to displays incorporating improved visual cues for indicating to an operator that a manual control input has been set to a desired set-point value within a predetermined tolerance.
2. Description of Related Art
Electronic instrumentation displays continue to advance in sophistication, achieving increasingly higher levels of information density and, consequently, presenting a greater amount of visual information to be perceived and understood by the operator. In many applications, it is critical that visual displays provide a proper cognitive mapping between what the operator is trying to achieve and the information available to accomplish the task. As a result, such systems increasingly utilize human-factor design principles in order to build instrumentation and controls that work cooperatively with human operators.
One area in particular that has experienced an increase in display complexity is the field of electronic flight system instrumentation. Accordingly, the Federal Aviation Administration (FAA) has promulgated a number of standards and advisory circulars relating to flight instrumentation. More particularly, Title 14 of the U.S. Code of Federal Regulations, Federal Aviation Regulations (FAR) Part 25, Sec. 25.1321 et seq. provides guidelines for arrangement and visibility of instruments, warning lights, indicators, and the like. Similarly, detailed guidelines related to electronic displays can be found in FAA Advisory Circular 20-88A, Guidelines on the Marking of Aircraft Powerplant Instruments (Sept. 1985).
In general, FAA regulations specify that flight instruments should be grouped together on the instrument panel and centered about the vertical plane of the pilot's forward vision. Furthermore, certain instruments--e.g., required power plant instruments--are to be closely grouped on the instrument panel. As instrument panel space is limited, achieving these goals can be quite difficult for designers faced with presenting a large amount of information within a relatively small space.
As a result of these and other challenges, present-day instrumentation systems are inadequate in many respects. For example, it is often difficult for an operator to judge whether a control input is set to a desired reference value. With continuous control inputs (as opposed to toggled or quantized inputs), this task typically requires the operator to compare the relative alignment of markers on dials or linear gauges. It may be necessary for the operator to adjust the control input such that the parameter value is "close enough" to a reference value within a specified tolerance. For example, an operator may be required to set the throttle input to a specified percentage value within a tolerance of +/-0.5%. Not surprisingly, it is extremely difficult for an operator to make this sort of quantitative judgment from a visual comparison of a pair of gauge markers.
This problem has traditionally been addressed by increasing the size of the display elements such that the elements themselves and the relationships between the elements are easier to perceive by the operator. Increasing the size of display elements, however, has the undesirable effect of reducing the effective information density of the display; that is, as the individual display elements increase in size, the area needed to display the entire instrument panel suffers a similar increase. Thus, the overriding goal of closely positioning the instruments within the operator's field of vision is not well served by increasing the size of individual display elements.